1. Field of the Invention
This invention relates to expandable, multipurpose digital and analog communication systems capable of providing a broad range of communication services to cable system users. Such cable systems embrace community antenna television (CATV) and closed circuit television (CCTV) networks as well as industrial, commericial and institutional broadband cable systems.
2. Description of the Prior Art
In my copending patent application, Ser. No. 125,440 now U.S. Pat. No. 4,326,289 entitled "Expandable Communications System" filed on Feb. 28, 1980, a system is described that employs a central station, a plurality of system stations that can be selectively addressed by the central station, and a bilateral transmission medium, e.g., a coaxial cable system, linking the system stations to the central station. At the central location a central controller has the capability of addressing a specific system station and of exchanging control and message information with any addressed system station. Each system station has a "main unit" that has a local input and a local output port and may also be connected over a parallel bus to a number of expansion modules which provide additional input and output ports. The input and output ports accommodate different communications services such as selective security surveillance, energy control, meter reading, text editing, data viewing, etc.
Because the system station is physically located on the premises of each customer served, the system station may be vulnerable to unauthorized tampering. Resistance against tampering is an especially desirable objective when the services to be provided by a CATV system include security functions or payment per TV channel or payment per individual program viewed by the CATV subscriber. To some extent the possibility of such tampering may be deterred by locating the system station outside of the customer's premises--as for example on a utility pole or within an underground cable vault. However, any such location of the system station would necessitate that a separate set of wires be provided between each port and the specific communications service at the customer's premises. A multiplicity of such wires would be unsightly, impractical and counter to the policy of having only a single, broad-band coaxial cable serve each customer's premises. It is therefore an object of my present invention to provide a communications system that is at least as flexible as the prior art system in its ability to accommodate a plurality of special communications services to various CATV customers but which is more secure against unauthorized tampering.
As the number of subscribers served by a CATV system increases so does the variety of services that may be demanded. It is expected, nevertheless, that the occupants of some premises along the cable right-of-way may have no desire to be supplied either with basic CATV television service or with any of the enhanced features that may require payments by the subscriber. Undoubtedly, however, even such a non-subscribing CATV "customer" will be a user of electric and water utilities and perhaps gas as well. Heretofore, reading of utility meters has been suggested as a natural concomitant of CATV service but the expense and complexity of on-site equipment has deterred the widespread installation of meter reading equipment. Even the expandable communications system described in the above mentioned patent application has shown itself to be economically unattrative for performing solely utility meter-reading functions at a particular premises. It is therefore an object of my invention to facilitate meter reading at subscriber's premises without regard to the degree of other CATV services that may be supplied at such premises.
Sophisticated CATV distribution networks, such as that described in the aforementioned "Expandable Communications System" include a headend control computer that may be programmed to conduct various diagnostic and maintenance checks which ascertain the status and operating parameters of the system stations. Occasionally, however, the nature of a specific trouble condition--such as intrusive noise in the upstream control signal communications channel--is such that the entire system control is affected. When such disruption occurs it is necessary to systematically isolate segments of the trunk cable and perhaps segments of the tributary distribution branches as well in order to locate the source of the intrusive signal(s). To some extent the strategic placement of bandstop filters throughout the cable network will limit upstream-channel intrusive noise from propagating throughout the distribution branches and trunk cables, however, it would be advantageous to automate the isolation process as a part of normal maintenance diagnostics routines. It is, therefore, another object of my invention to facilitate the automatic switching control of segments of the cable network itself.
As hereinbefore noted the provision of multifarious premium services will undoubtedly entail a special schedule of tariffs. Among these may be pay-per-channel or pay-per-program charges. Heretofore, the provision of such services has been by way of cable drop restrictors, one such restrictor being required per service with no convenient way to regulate a discrete viewing period over the drop. Sophisticated scrambler/descrambler systems often including addressability to the specific subscriber and service have been employed. These implementations utilize decoding and descrambling equipment within the subscriber premises making these devices extremely vulnerable to unauthorized tampering. It is therefore a further object of my invention to provide selectively controllable, readily changeable and highly tamper resistant channel access at any drop on an automated and centralized basis.